I have been using a similar idea for many years. Around here you can get 3' x 3' x 18" blocks of really compressed foam that they place under fishing and boating docks to float them. Usually you can find stray ones floating in coves or along the shore while fishing or on the lakeside when people are upgrading thier docks. If I have a bad year finding one and really need a new one I can buy them for like $10 usualy from any dock builder by the lake.
They hold up really well to FP and BH. I never thought of wrapping them to keep some of the mess down. With all the flooding we have had lately I have found about 15 good chunks so far I should be set for another 30 years or so. lol
Tom